In automatic arc welding a welding torch is made to weave along the weld line of base metals to be welded, and simultaneously, an arc current caused by the weaving is detected by an arc sensor to compensate movement of the welding torch, and thereby the weld line of the base metals is automatically arc welded. More specifically, when the actual weld line of the base metals to be welded deviates from an instructed weld line, the arc current is detected by the arc sensor and processed and thereby the movement of the welding torch is compensated to correctly move the welding torch along the actual weld line.
In the processing of an arc current of a conventional control apparatus for an automatic arc welding machine, for example, the position, amplitude, and the like of an arc current detected by the arc sensor are monitored, and welding torch is moved for a predetermined distance in accordance with the peak value of the monitored position, amplitude, and the like, and as a result, the welding torch is moved along the actual weld line of the base metals.
An arc current detected by an arc sensor has an unstable waveform because of disturbances occurring during arc welding and the like. In particular, although the peak value of the ac current is processed by smoothing the current waveform thereof through a filter or the like, a change in the arc current caused by a deviation of the welding torch from the weld line of the base metals cannot be easily discriminated from a change in the arc current caused by a disturbance or the like. Furthermore, a peak can occur in an arc current due to factors other than a deviation of the welding torch from the weld line, and as a result, an overcompensation of the movement of the welding torch occurs.